Method and apparatus for measuring a parameter of a fluid flowing within a pipe

ABSTRACT

A method and apparatus for determining at least one characteristic of a fluid flowing within a pipe is provided and includes at least one sensing device. The at least one sensing device includes a first sensor segment having a first segment polarity and being associated with a first outer portion of the pipe and a second sensor segment having a second segment polarity and being associated with a second outer portion of the pipe, wherein the first sensor segment and the second sensor segment generate sensor data responsive to the fluid flowing within the pipe. The apparatus further includes a processing device communicated with the at least one sensing device, wherein the processing device receives the sensor data and processes the sensor data to determine the at least one characteristic of the fluid.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

The present application claims the benefit of U.S. Provisional PatentApplication No. 60/703,940, (CiDRA Docket No. CC-0822) filed Jul. 29,2005, which is incorporated by reference herein in its entirety.

TECHNICAL FIELD OF THE INVENTION

This invention relates generally to measuring a parameter of a fluid andmore particularly to a method and apparatus for measuring a parameter ofa fluid such as velocity and volumetric flow rate of the flow within apipe.

BACKGROUND OF THE INVENTION

A fluid flow process (flow process) includes any process that involvesthe flow of fluid through pipes, ducts, or other conduits, as well asthrough fluid control devices such as pumps, valves, orifices, heatexchangers, and the like. Flow processes are found in many differentindustries such as the oil and gas industry, refining, food and beverageindustry, chemical and petrochemical industry, pulp and paper industry,power generation, pharmaceutical industry, and water and wastewatertreatment industry. The fluid within the flow process may be a singlephase fluid (e.g., gas, liquid or liquid/liquid mixture) and/or amulti-phase mixture (e.g. paper and pulp slurries or other solid/liquidmixtures). The multi-phase mixture may be a two-phase liquid/gasmixture, a solid/gas mixture or a solid/liquid mixture, gas entrainedliquid or a three-phase mixture.

Currently, various sensing technologies exist for measuring variousphysical parameters of fluids in an industrial flow process. Suchphysical parameters may include, for example, velocity, volumetric flowrate, composition, gas volume fraction, consistency, density, and massflow rate. One such sensing technology is described in commonly-ownedU.S. Pat. No. 6,609,069 to Gysling, entitled “Method and Apparatus forDetermining the Flow Velocity Within a Pipe”, which is incorporatedherein by reference. The '069 patent describes a method andcorresponding apparatus for measuring the flow velocity of a fluid in anelongated body (pipe) by sensing vortical disturbances convecting withthe fluid. The method includes the steps of providing an array of atleast two sensors disposed at predetermined locations along theelongated body, wherein each sensor samples the pressure of the fluid atthe position of the sensor at a predetermined sampling rate. The sampleddata from each sensor at each of a number of instants of time spanning apredetermined sampling duration is accumulated and at least a portion ofa so called k-ω plot is constructed from the accumulated sampled data,wherein the k-ω plot is indicative of a dispersion relation for thepropagation of acoustic pressures emanating from the vorticaldisturbances. A convective ridge in the k-ω plot is identified and theorientation of the convective ridge in the k-ω plot is determined. Theflow velocity based on a predetermined correlation of the flow velocitywith the slope of the convective ridge of the k-ω plot may then bedetermined from this information.

Such sensing technology is effective in determining various parametersof a fluid flow within a pipe. However, as with any computationallycomplex process, there remains a desire to increase computationalefficiency, accuracy and robustness.

Unfortunately, in some situations flow measurements may be corrupted,degraded or they may not be able to be obtained at all due to thepresence of unwanted signals masking the convective ridge (or vorticalflow ridge). This unwanted energy can obscure or mask the energy of theconvective ridge, and therefore, make it difficult or even impossible toisolate the energy of the convective ridge to determine the slope of theridge. For example, the current geometry for sensors that sense vorticaldisturbances convecting with the fluid include sensors that provide 360°coverage of the pipe. This is undesirable for several reasons. First,the asymmetric bending modes create an equal and opposite deformation ofthe sensor, so no signal is created due to sensor deformation. Second,because acoustic signals (acoustic modes create a uniform distortion)and signals due to pressure pulses and pipe fluids having uniformlyvarying temperatures are created, the signals due to vorticaldisturbances may be degraded.

SUMMARY OF THE INVENTION

An apparatus for determining at least one characteristic of a fluidflowing within a pipe is provided and includes at least one sensingdevice. The at least one sensing device includes a first sensor segmenthaving a first segment polarity and being associated with a first outerportion of the pipe and a second sensor segment having a second segmentpolarity and being associated with a second outer portion of the pipe,wherein the first sensor segment and the second sensor segment generatesensor data responsive to the fluid flowing within the pipe. Theapparatus further includes a processing device communicated with the atleast one sensing device, wherein the processing device receives thesensor data and processes the sensor data to determine the at least onecharacteristic of the fluid.

A method for determining at least one characteristic of a fluid flowingwithin a pipe is provided and includes receiving sensor data from atleast one sensing device, wherein the at least one sensing deviceincludes a first sensor segment and a second sensor segment disposed inthe same axially plane and wherein the first sensor segment isassociated with a first outer portion of the pipe and a second sensorsegment is associated with a second outer portion of the pipe. Themethod further includes processing the sensor data to generate the atleast one characteristic of the fluid flowing within the pipe.

A sensing device for determining at least one characteristic of a fluidflowing within a pipe is provided and includes a first sensor segmentand a second sensor segment, wherein the first sensor segment and thesensor second segment are associated with the pipe to measure unsteadypressure associated with the fluid flow and configured to filter out atleast one of acoustic mode signals and bending mode signals.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring now to the drawings, the foregoing and other features andadvantages of the present invention will be more fully understood fromthe following detailed description of illustrative embodiments, taken inconjunction with the accompanying drawings in which like elements arenumbered alike:

FIG. 1 is schematic diagram of an apparatus for determining at least oneparameter associated with a fluid flowing in a pipe.

FIG. 2 is a cross-sectional view of a sensor of FIG. 1 disposed on thepipe.

FIG. 3 is a block diagram of a flow logic used in the apparatus of thepresent invention.

FIG. 4 is a k-ω plot of data processed from an apparatus embodying thepresent invention that illustrates slope of the convective ridge, and aplot of the optimization function of the convective ridge.

FIG. 5 is schematic diagram of an apparatus embodying the presentinvention for determining at least one parameter associated with a fluidflowing in a pipe.

FIG. 6 is a cross-sectional view of a sensor of FIG. 5 disposed on thepipe.

FIG. 7 is a schematic view of the electrical connections of the segmentsof the sensor of FIG. 6.

FIG. 8 is schematic diagram of an embodiment of an apparatus embodyingthe present invention for determining at least one parameter associatedwith a fluid flowing in a pipe.

FIG. 9 is a cross-sectional view of a sensor of FIG. 8 disposed on thepipe.

FIG. 10 is schematic diagram of an embodiment of an apparatus embodyingthe present invention for determining at least one parameter associatedwith a fluid flowing in a pipe.

FIG. 11 is a cross-sectional view of a sensor of FIG. 10 disposed on thepipe.

DETAILED DESCRIPTION

As discussed briefly hereinabove and described in commonly-owned U.S.Pat. No. 6,609,069 to Gysling, entitled “Method and Apparatus forDetermining the Flow Velocity Within a Pipe”, and U.S. Pat. No.6,889,562, each of which are incorporated herein by reference in theirentireties, unsteady pressures along a pipe caused by coherentstructures (e.g., turbulent eddies and vortical disturbances) thatconvect with a fluid flowing in the pipe contain useful informationregarding parameters of the fluid. The present invention providesvarious means for using this information to measure parameters of afluid flow, such as, for example, velocity and volumetric flow rate.

Referring to FIGS. 1-4, an apparatus for measuring the velocity and/orvolumetric flow of a fluid flowing within a pipe is shown, wherein theapparatus is similar to that described in U.S. Pat. No. 6,609,069, U.S.Pat. No. 6,889,562, U.S. patent application Ser. No. 10/712,818, filedon Nov. 12, 2003, and U.S. patent application Ser. No. 10/712,833, filedon Nov. 12, 2003, which are incorporated herein by reference.

Referring to FIG. 1, the apparatus 100 measures at least one parameterassociated with a flow 102 flowing within a duct, conduit or other formof pipe 104, wherein the parameter of the flow 102 may include, forexample, at least one of the velocity of the flow 102 and the volumetricflow rate of the flow 102. The flow 102 is shown passing through thepipe 104, wherein the flow 102 is depicted as a non-stratified,Newtonian flow operating in the turbulent regime at Reynolds numbersabove about 100,000. The flow 102 has a velocity profile 106 that isuniformly developed from the top of the pipe 104 to the bottom of thepipe 104. Furthermore, the coherent structures 108 in thenon-stratified, turbulent, Newtonian flow 102 exhibit very littledispersion. In other words, the speed of convection of the coherentstructures 108 is not strongly dependent on the physical size of thestructures 108. It should be appreciated that, as used herein,dispersion describes the dependence of convection velocity withwavelength, or equivalently, with temporal frequency. It should also beappreciated that flows for which all wavelengths convect at a constantvelocity are termed “non-dispersive” and for turbulent, Newtonian flow,there is typically not a significant amount of dispersion over a widerange of wavelength to diameter ratios.

While the flow 102 is depicted as having a uniform velocity profile, itshould be appreciated that the present invention may be used to measurestratified flows 102. Stratified flow 102 has a velocity profile 106that is skewed from the top of the pipe 104 to the bottom of the pipe104, as may be found in industrial fluid flow processes involving thetransportation of a high mass fraction of high density, solid materialsthrough a pipe 104 where the larger particles travel more slowly at thebottom of the pipe 104. For example, the flow 102 may be part of ahydrotransport process.

The apparatus 100 of FIG. 1 accurately measures parameters such asvelocity and volumetric flow rate of a stratified flow and/ornon-stratified flow 102, wherein the apparatus 100 may include a spatialarray 110 of at least two sensors 112 disposed at different axiallocations x₁ . . . x_(N) along the pipe 104. Each of the sensors 112provides a pressure signal P(t) indicative of unsteady pressure createdby coherent structures convecting with the flow 102 within the pipe 104at a corresponding axial location x₁ . . . x_(N) of the pipe 104. Thepressure generated by the convective pressure disturbances (e.g., eddies108) may be measured through strained-based sensors 112 and/or pressuresensors 112. The sensors 112 provide analog pressure time-varyingsignals P₁(t), P₂(t), P₃(t) . . . P_(N)(t) to a signal processor 114,which determines the parameter of the flow 102 using pressure signalsfrom the sensors 112, and outputs the parameter as a signal 116.

While the apparatus 100 is shown as including four sensors 112, it iscontemplated that the array 110 of sensors 112 includes two or moresensors 112, each providing a pressure signal P(t) indicative ofunsteady pressure within the pipe 104 at a corresponding axial locationX of the pipe 104. For example, the apparatus may include 2, 3, 4, 5, 6,7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, or 24sensors 112. Generally, the accuracy of the measurement improves as thenumber of sensors 112 in the array 110 increases. Thus, the degree ofaccuracy provided by the greater number of sensors 112 is offset by theincrease in complexity and time for computing the desired outputparameter of the flow 102 and the number of sensors 112 used isdependent at least in part on the degree of accuracy desired and thedesire update rate of the output parameter provided by the apparatus100.

The signals P₁(t) . . . P_(N)(t) provided by the sensors 112 in thearray 110 are processed by the signal processor 114, which may be partof a larger processing unit 118. For example, the signal processor 114may be a microprocessor and the processing unit 118 may be a personalcomputer or other general purpose computer. It is contemplated that thesignal processor 114 may be any one or more analog or digital signalprocessing devices for executing programmed instructions, such as one ormore microprocessors or application specific integrated circuits(ASICS), and may include memory for storing programmed instructions, setpoints, parameters, and for buffering or otherwise storing data.

The signal processor 114 may output the one or more parameters 116 to adisplay 120 or another input/output (I/O) device 122. The I/O device 122may also accept user input parameters. The I/O device 122, display 120,and signal processor 114 unit may be mounted in a common housing, whichmay be attached to the array 110 by a flexible cable, wirelessconnection, or the like. The flexible cable may also be used to provideoperating power from the processing unit 118 to the array 110 ifnecessary.

To determine the one or more parameters 116 of the flow 102, the signalprocessor 114 applies the data from the sensors 112 to flow logic 124executed by the signal processor 114. Referring to FIG. 3, an example offlow logic 124 is shown. Some or all of the functions within the flowlogic 124 may be implemented in software (using a microprocessor orcomputer) and/or firmware, or may be implemented using analog and/ordigital hardware, having sufficient memory, interfaces, and capacity toperform the functions described herein.

The flow logic 124 may include a data acquisition unit 126 (e.g., A/Dconverter) that converts the analog signals P₁(t) . . . P_(N)(t) torespective digital signals and provides the digital signals P₁(t) . . .P_(N)(t) to FFT logic 128. The FFT logic 128 calculates the Fouriertransform of the digitized time-based input signals P₁(t) . . . P_(N)(t)and provides complex frequency domain (or frequency based) signalsP₁(ω), P₂(ω), P₃(ω), . . . P_(N)(ω) indicative of the frequency contentof the input signals. Instead of FFT's, any other technique forobtaining the frequency domain characteristics of the signalsP₁(t)−P_(N)(t), may be used. For example, the cross-spectral density andthe power spectral density may be used to form a frequency domaintransfer functions (or frequency response or ratios) discussedhereinafter.

One technique of determining the convection velocity of the coherentstructures (e.g., turbulent eddies) 108 within the flow 102 is bycharacterizing a convective ridge of the resulting unsteady pressuresusing an array of sensors or other beam forming techniques, similar tothat described in U.S. patent application Ser. No. 09/729,994, filedDec. 4, 2000, now U.S. Pat. No. 6,609,069, which is incorporated hereinby reference in its entirety. A data accumulator 130 accumulates thefrequency signals P₁(ω)−P_(N)(ω) over a sampling interval, and providesthe data to an array processor 132, which performs a spatial-temporal(two-dimensional) transform of the sensor data, from the x-t domain tothe k-ω domain, and then calculates the power in the k-ω plane, asrepresented by a k-ω plot (FIG. 4).

The array processor 132 uses standard so-called beam forming, arrayprocessing, or adaptive array-processing algorithms, i.e. algorithms forprocessing the sensor signals using various delays and weighting tocreate suitable phase relationships between the signals provided by thedifferent sensors, thereby creating phased antenna array functionality.In other words, the beam forming or array processing algorithmstransform the time domain signals from the sensor array into theirspatial and temporal frequency components, i.e. into a set of wavenumbers given by k=2π/λ, where λ is the wavelength of a spectralcomponent, and corresponding angular frequencies given by ω=2πν.

The prior art teaches many algorithms of use in spatially and temporallydecomposing a signal from a phased array of sensors, and the presentinvention is not restricted to any particular algorithm. One particularadaptive array processing algorithm is the Capon method/algorithm. Whilethe Capon method is described as one method, the present inventioncontemplates the use of other adaptive array processing algorithms, suchas MUSIC algorithm. The present invention recognizes that suchtechniques can be used to determine flow rate, i.e. that the signalscaused by a stochastic parameter convecting with a flow are timestationary and have a coherence length long enough that it is practicalto locate sensors 112 apart from each other and yet still be within thecoherence length.

Convective characteristics or parameters have a dispersion relationshipthat can be approximated by the straight-line equation,k=ω/u,  (Eqn. 1)where u is the convection velocity (flow velocity). A plot of k-ω pairsobtained from a spectral analysis of sensor samples associated withconvective parameters portrayed so that the energy of the disturbancespectrally corresponding to pairings that might be described as asubstantially straight ridge, a ridge that in turbulent boundary layertheory is called a convective ridge. As will be described hereinafter,as the flow becomes increasingly dispersive, the convective ridgebecomes increasingly non-linear. What is being sensed are not discreteevents of coherent structures 108, but rather a continuum of possiblyoverlapping events forming a temporally stationary, essentially whiteprocess over the frequency range of interest. In other words, theconvective coherent structures 108 are distributed over a range oflength scales and hence temporal frequencies.

To calculate the power in the k-ω plane, as represented by a k-ω plot(see FIG. 4) of either the signals, the array processor 132 determinesthe wavelength and so the (spatial) wavenumber k, and also the(temporal) frequency and so the angular frequency ω, of various of thespectral components of the stochastic parameter. There are numerousalgorithms available in the public domain to perform thespatial/temporal decomposition of arrays of sensors 112. It should beappreciated that the present embodiment may use temporal and spatialfiltering to precondition the signals to effectively filter out thecommon mode characteristics Pcommon mode and other long wavelength(compared to the sensor spacing) characteristics in the pipe 104 bydifferencing adjacent sensors 112 and retain a substantial portion ofthe stochastic parameter associated with the flow field and any othershort wavelength (compared to the sensor spacing) low frequencystochastic parameters.

In the case of suitable coherent structures 108 being present, the powerin the k-ω plane shown in a k-ω plot of FIG. 4 shows a convective ridge138. The convective ridge represents the concentration of a stochasticparameter that convects with the flow and is a mathematicalmanifestation of the relationship between the spatial variations andtemporal variations described above. Such a plot will indicate atendency for k-ω pairs to appear more or less along a line 138 with someslope, the slope indicating the flow velocity.

Once the power in the k-ω plane is determined, a convective ridgeidentifier 134 uses one or another feature extraction method todetermine the location and orientation (slope) of any convective ridge138 present in the k-ω plane. For example, in one embodiment, aso-called slant stacking method is used, a method in which theaccumulated frequency of k-ω pairs in the k-ω plot along different raysemanating from the origin are compared, each different ray beingassociated with a different trial convection velocity (in that the slopeof a ray is assumed to be the flow velocity or correlated to the flowvelocity in a known way). The convective ridge identifier 134 providesinformation about the different trial convection velocities, informationreferred to generally as convective ridge information. An analyzer 136examines the convective ridge information including the convective ridgeorientation (slope) and assuming the straight-line dispersion relationgiven by k=ω/u, the analyzer 136 determines the flow velocity and/orvolumetric flow, which are output as parameters 116. The volumetric flowmay be determined by multiplying the cross-sectional area of the insideof the pipe 104 with the velocity of the process flow 102.

As previously noted, for turbulent, Newtonian fluids, there is typicallynot a significant amount of dispersion over a wide range of wavelengthto diameter ratios. As a result, the convective ridge 138 in the k-ωplot is substantially straight over a wide frequency range and,accordingly, there is a wide frequency range for which the straight-linedispersion relation given by k=ω/u provides accurate flow velocitymeasurements. For stratified flows, however, some degree of dispersionexists such that coherent structures 108 convect at velocities whichdepend on their size. As a result of increasing levels of dispersion,the convective ridge 138 in the k-ω plot becomes increasinglynon-linear. Thus, unlike the non-dispersive flows, determining the flowrate of a dispersive mixture by tracking the speed at which coherentstructures 108 convect requires a methodology that accounts for thepresence of significant dispersion, as described in greater detail inU.S. patent application Ser. No. 11/077,709, filed on Mar. 10, 2005,which is incorporated herein by reference.

In the embodiment shown in FIG. 1 and FIG. 2, each of the sensors 112 isformed by a strip of piezoelectric material 140 such as, for example,the polymer, polarized fluoropolymer, PVDF, which measures the straininduced within the pipe 104 due to the coherent structures convectingwith the flow 102, similar to that described in U.S. patent applicationSer. No. 10/712,818 and U.S. Provisional patent application Ser. No.10/712,833, which are incorporated herein by reference. The sensors 112can be formed from PVDF films, co-polymer films, or flexible PZTsensors, similar to that described in “Piezo Film Sensors technicalManual” provided by Measurement Specialties, Inc. of Fairfield, N.J.,which is incorporated herein by reference. The PVDF sensors include PVDFmaterial disposed between a pair of conductive layers (FIG. 7). Theconductive layers are electrically connected to a processor by a pair oftwisted wires, wherein the conductive layer may be formed of silver ink.The strips of piezoelectric film material forming the sensors 112 alongeach axial location x₁ . . . x_(N) of the pipe 104 may be adhered to thesurface of a steel strap 142 (e.g., a hose clamp) that extends aroundand clamps onto the outer surface of the pipe 104. As discussedhereinafter, other types of sensors 112 and other methods of attachingthe sensors 112 to the pipe 104 may be used.

As best shown in FIG. 2, the PVDF material 140 of each sensor 112 isdisposed substantially around the circumference of the pipe 104, whichenables the sensing material 140 to measure pressure disturbancesattributed to the convective vortices 106 propagating with the fluidflow 102. Advantageously, the configuration of the sensing materialbeing disposed substantially around the circumference of the pipe 104filters out pressure disturbances associated with vibration and otherbending modes of the pipe 104. Unfortunately, the sensors 112 also senseunsteady pressure attributed to acoustic pressures or noise within thepipe 104, wherein the measurement of these acoustic pressures decreasesthe signal to noise ratio when measuring the convective turbulence 106.

As discussed briefly hereinabove, in the geometry of the sensors 112 (inFIG. 2), asymmetric bending modes create equal and opposite deformationof the sensor 112 and therefore create no signal. Acoustic modes createa uniform distortion, and therefore create a signal along with a signalassociated with vortical disturbances. (We might expect the acousticsignal to scale with the sensor length and the vortical signal to scaleas the square root of the sensor length.) Additionally, pressure pulsesand pipe fluids with uniform varying temperatures should also producesignals in this configuration. These signals, i.e. signals from theacoustic pressures, the pressure pulses, and the varying temperaturefluids may degrade the measurement of the vortical pressure disturbance(vortical signals).

One method of filtering the acoustic noise is to difference the signalsof adjacent sensors 112. While this increases the signal to noise ratio,it would be advantageous if each sensor 112 had the ability to filterboth the unsteady pressures associated with the bending modes of thepipe 104 and the acoustic noise (or pressure field).

Referring to FIG. 5 and FIG. 6, an apparatus 200 in accordance with thepresent invention is illustrated. The apparatus 200 includes a sensorarray 110 having at least one sensor 212 having a geometry such thateach sensor 212 includes four segments (or sections) of PVDF (or otherstrain-based sensor material), wherein the segments are labeled A, B, Cand D. As shown in FIG. 5, it can be seen that although segment A hasthe same polarity as segment B and segment C has the same polarity assegment D the segment pair AB has a different polarity than the segmentpair CD. Thus, because segment pair AB has an opposite polarity thansegment pair CD, the signals from this configuration are different fromthe configuration of FIG. 2. Moreover, in the geometry of FIG. 5,acoustic signals (and any other common mode signals, like thosegenerated by pressure pulses or varying temperature fluids) arecancelled out.

Specifically in the embodiment shown, the sensors 112 extend over anarcuate outer surface of the pipe 104 defined by the angle θ. Forexample, each of the sensors 112 may extend about ¼ of the circumferenceof the pipe 104, wherein each pair of opposing sensors (AB and CD)measure the vortical disturbance (or other unsteady pressures thatpropagate with the flow). However, similar to that described with regardto FIG. 1 and FIG. 2, the opposing sensor sections (pair CD and pair AB)have the same polarity and therefore they provide a signal that filtersout the asymmetric bending modes and because the opposing sections ABhave an opposite polarity of the opposing sections CD, the acousticpressure signals, temperature signals and other common mode signals arefiltered out. Furthermore, referring to FIG. 7, to advantageouslyminimize the time to process the signals, the sensor sections (AB andCD) of each sensor 112 may be electrically connected in series toprovide one signal to the processor 118. Alternatively, each pair ofsignals may be electrically connected together to provide two signalsfrom each sensor 112 to the processor 118. It should be appreciated thatthe configuration of FIG. 6 may perform better in situations wherecommon mode signals are limiting performance. For example in somesituations we either have to reduce the gain of the sensor signals (andhave poor signal to noise ratio) or keep the gain high and risksaturating the amplifiers because high acoustic levels or pressurepulses are present. It should be further appreciated that FIG. 7illustrates only one embodiment of the electrical connections of asensor shown in FIG. 5 and FIG. 6 and other embodiments may be used.

While the apparatus 200 is shown as including four sensors 112, it iscontemplated that each array 110 may include two or more sensors 112,with each sensor 112 providing a pressure signal P(t) indicative ofunsteady pressure within the pipe 104 at a corresponding axial locationX of the pipe 104. For example, the apparatus may include 2, 3, 4, 5, 6,7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, or 24sensors 112. Generally, the accuracy of the measurement improves as thenumber of sensors 112 in the array increases. The degree of accuracyprovided by the greater number of sensors 112 is offset by the increasein complexity and time for computing the desired output parameter of theflow 102. Therefore, the number of sensors 112 used is dependent atleast on the degree of accuracy desired and the desire update rate ofthe output parameter provided by the apparatus 200.

It should be appreciated that while the embodiment of FIGS. 5-7 of thepresent invention illustrate a sensor 112 having four segments, theinvention contemplates a sensor having any number of sensor segments(for example, segments A-L) wherein the sensors may be of any lengthprovided the following relationships are met. For sensor configurationsthat filter the acoustic signals, temperature signals and other commonmode signals, the relationship may be given by, $\begin{matrix}{{{\int_{0}^{2\pi}{{ɛ(\theta)}{\mathbb{d}\theta}}} = 0},} & ( {{Eqn}.\quad 2} )\end{matrix}$wherein ε(θ) is equal to the signal power (e.g. area, length). In otherwords the sum of all the signals provided by the sensors 112 around thecircumference of the pipe 104 should equal zero. Basically, the negativepolarity sensor segments must be equal in length or area around the pipecircumference as the positive polarity sensor segments. For sensorconfigurations that filter the bending mode signals, the relationshipmay be given by: $\begin{matrix}{{{\int_{\pi + 0}^{\theta + \pi}{{ɛ(\theta)}{\mathbb{d}\theta}}} = {\int_{\theta + \pi}^{\theta + {2\pi}}{{ɛ(\theta)}{\mathbb{d}\theta}}}},} & ( {{Eqn}.\quad 3} )\end{matrix}$wherein ε(θ) is equal to the signal power (e.g. area, length). In otherwords, at any given angle or θ, the sensor sections length or area onone half the pipe 104 is equal to the sensor sections length or area onthe opposing other half of the pipe 104.

For example, as given by Equation 2 hereinbefore, to create a sensor 112that filters out the acoustic signals, the sensor is configured suchthat the sum of the signals generated by the sensor 112 around thecircumference of the pipe 104 should equal zero. This may beaccomplished by arranging the sensor(s) 112 such that the negativepolarity sensor segments are equal in length or area around thecircumference of the pipe 104 to the positive polarity sensor segments.In a similar fashion and as given by Equation 3, to create a sensor 112that filters out the bending mode signals, the sensor segments have thesame polarity and is configured such that, at any given angle or θ, thesurface area of the sensor segments or the length of the sensor segmentson one side of the pipe is substantially equal to the surface area ofthe sensor segments or the length of the sensor segments on the opposingside of the pipe.

Accordingly, to create a sensor 112 that filters out both of theacoustic signals and the bending mode signals, the sensor 112 should beconfigured to satisfy both of the aforementioned conditions, i.e.Equations 2 and 3. Two such configurations can be seen by referring toFIG. 6 and FIG. 8 and FIG. 9 which filter out both the bending modesignals and the acoustic signals. As shown in FIG. 8 and FIG. 9, thesensor 250 includes a plurality of segments 112 (in this case twelve)disposed around the outer surface of the pipe 104, wherein six of thesegments A(+), C(+), E(+), G(+), I(+), K(+) have a positive polarity andsix of the segments B(−), D(−), F(−), H(−), J(−), L(−) have a negativepolarity and wherein the segments are arranged such that no two segmentshaving the same polarity are disposed adjacent each other. It should beappreciated that while the sensors in FIG. 8 and FIG. 9 are shown asalternating in polarity, it is not necessary to satisfy the conditionsof Equations 2 and 3.

Thus, in a similar fashion to FIG. 6, the configuration in FIG. 8 andFIG. 9 filters out the bending mode signals because the sensor segments112 are associated with the pipe 104 such that, at any given angle or θ,the polarity of the opposing sensors are the same and the aggregatelength of the sensor segments 112 and/or the aggregate area of thesensor segments 112 on one half of the pipe 104 is equal to theaggregate length of the sensor segments 112 and/or the aggregate area ofthe sensor segments 112 on the other half of the pipe 104. Additionally,the acoustic signals are filtered out because the sum of the signalsfrom the sensor segments 250 of one polarity and the signals from thesensor segments 250 of the opposite polarity are essentially equal tozero.

On the other hand, while one of the preferred embodiments may includesensor segments to filter both acoustic signals (or temperature or othercommon mode signals) and bending mode signals, the present inventionalso contemplates segmented sensors 112 that filter only acousticsignals or only bending mode signals. For example, the sensor 112 inFIG. 2 is configured to filter only the bending mode signals. This isbecause the sensor 112 in FIG. 2 is associated with the pipe 104 suchthat, at any given angle or θ, the polarity of the sensors are the sameand the length of the sensor 112 and/or the area of the sensor 112 onone half of the pipe 104 is equal to the length of the sensor 112 and/orthe area of the sensor 112 on the other half of the pipe 104.

Alternatively, the embodiment 300 as shown in FIG. 10 and FIG. 11 isconfigured to primarily filter out the acoustic modes as opposed to thebending modes. This is because the sensor segments 302 are of oppositepolarity and are associated with the pipe 104 such that the sum of allthe signals provided by the sensor segments 302 around the circumferenceof the pipe 104 are essentially equal to zero. As shown in FIG. 10 andFIG. 11, the embodiment 300 is shown wherein the segments 302 of thesensor 112 may have opposite polarities and the same length or area tofilter the acoustic signals, temperature signals and other common modesignals. This configuration may be sufficient for applications whereinthe vibration or bend of the pipe 104 is minimal and while the segmentsare shown opposing each other, the present invention contemplates thatthe segments do not have to be opposite of each other and may bedisposed in any configuration suitable to the desired end purpose. Forexample, the configuration of the segments of the bands may be disposedanywhere along the circumference of the pipe 104 provided therelationship described hereinbefore is met.

Similarly, the segments of the sensor 112 may be of the same polarityand disposed opposing each other and may have the same length or area tofilter out the bending mode signals. This configuration may besufficient wherein acoustic noise, temperature variations, or othercommon mode signals are minimal. As above, the segments may be disposedin any configuration suitable to the desired end purpose and thus may bedisposed in any manner provided the relationship described hereinbeforeis met.

It should be appreciated that any configuration satisfying Equation 2and Equation 3 may be used, suitable to the desired end purpose. Forexample, referring again to FIG. 6, the sensors 112 describedhereinabove may be arranged to primarily filter out the bending modesignals or primarily filter out the acoustic signals. As can be seen, ifthe sensor segments in FIG. 6 were configured to be of the samepolarity, then sensor segments of FIG. 6 would only filter out thebending mode signals. Alternatively, if the sensor segments wereconfigured such that sensor segment B were of a positive polarity (i.e.B(+)) and sensor segment D were of a negative polarity (i.e. D(−)), thenthe sensor segments would only filter out the acoustic signals, andwould function similar to the embodiment shown in FIG. 11.

Additionally, the sensor segments may be arranged to measure signalsresponsive to a desired portion of the flow 102 within the pipe 104. Itshould be appreciated that for situations where a measurement of aportion of the flow is desired, such as where a stratified flow ispresent, the sensor segments can be arranged to measure the signals in adesired portion of the pipe 104 to obtain a desired flow ratemeasurement. For example, when a stratified flow is present is may bedesirable to obtain a flow rate measurement for the middle portion ofthe pipe (i.e. nominal flow rate measurement). As such, the sensors maybe configured in a plurality of configurations. For example, referringto FIG. 10, in the case of a stratified flow mentioned hereinbefore, thesensors may be disposed around only the middle portion of the pipe.Alternatively, similar results may be obtained by disposing the sensorsegments in FIG. 9 to be disposed in the area of the middle portion ofthe pipe 104. For example, sensor segments D and J, and/or C and Iand/or K and E may be used, wherein the sensor segment pairs are ofopposite polarity. Alternative, sensors D and J may be used. One willappreciate that the circumferential length of the sensors will determinethe portion of the flow that will be measured, similar to that describedin U.S. patent application Ser. No. 11/077,709, filed on Mar. 10, 2005,which is incorporated herein by reference.

It should be appreciated that in any of the embodiments describedherein, the sensors 112 may include electrical strain gages, opticalfibers and/or gratings, ported sensors, ultrasonic sensors, among othersas described herein, and may be attached to the pipe by adhesive, glue,epoxy, tape or other suitable attachment means to ensure suitablecontact between the sensor 112 and the pipe 104. The sensors 112 mayalternatively be removable or permanently attached via known mechanicaltechniques such as mechanical fastener, spring loaded, clamped, clamshell arrangement, strapping or other equivalents. Alternatively, straingages, including optical fibers and/or gratings, may be embedded in acomposite pipe 104. If desired, for certain applications, gratings maybe detached from (or strain or acoustically isolated from) the pipe 104if desired. It is also contemplated that any other strain sensingtechnique may be used to measure the variations in strain in the pipe104, such as highly sensitive piezoelectric, electronic or electric,strain gages attached to or embedded in the pipe 104.

It should be further appreciated that in various embodiments of thepresent invention, a piezo-electronic pressure transducer may be used asone or more of the pressure sensors and it may measure the unsteady (ordynamic or ac) pressure variations inside the pipe 104 by measuring thepressure levels inside the pipe 104. For example, in one embodiment ofthe present invention, the sensors 112 may comprise pressure sensorsmanufactured by PCB Piezotronics of Depew, N.Y. and/or may includeintegrated circuit piezoelectric voltage mode-type sensors that featurebuilt-in microelectronic amplifiers, and convert the high-impedancecharge into a low-impedance voltage output. Specifically, a Model 106Bmanufactured by PCB Piezotronics is used which is a high sensitivity,acceleration compensated integrated circuit piezoelectric quartzpressure sensor suitable for measuring low pressure acoustic phenomenain hydraulic and pneumatic systems. It has the unique capability tomeasure small pressure changes of less than 0.001 psi under high staticconditions. The 106B has a 300 mV/psi sensitivity and a resolution of 91dB (0.0001 psi).

The sensors 112 may incorporate a built-in MOSFET microelectronicamplifier to convert the high-impedance charge output into alow-impedance voltage signal. The sensors 112 may be powered from aconstant-current source and can operate over long coaxial or ribboncable without signal degradation. It should be appreciated that thelow-impedance voltage signal is not affected by triboelectric cablenoise or insulation resistance-degrading contaminants and power tooperate integrated circuit piezoelectric sensors generally takes theform of a low-cost, 24 to 27 VDC, 2 to 20 mA constant-current supply.Most piezoelectric pressure sensors are constructed with eithercompression mode quartz crystals preloaded in a rigid housing, orunconstrained tourmaline crystals. These designs advantageously give thesensors microsecond response times and resonant frequencies in thehundreds of kHz, with minimal overshoot or ringing, wherein smalldiaphragm diameters ensure spatial resolution of narrow shock waves.

Additionally, the output characteristic of piezoelectric pressure sensorsystems is that of an AC-coupled system, where repetitive signals decayuntil there is an equal area above and below the original base line. Asmagnitude levels of the monitored event fluctuate, the output remainsstabilized around the base line with the positive and negative areas ofthe curve remaining equal.

Furthermore it is contemplated that each of the sensors 112 may includea piezoelectric sensor that provides a piezoelectric material to measurethe unsteady pressures of the flow 102. The piezoelectric material, suchas the polymer, polarized fluoropolymer, PVDF, measures the straininduced within the process pipe 104 due to unsteady pressure variationswithin the flow 102. Strain within the pipe 104 is transduced to anoutput voltage or current by the attached piezoelectric sensors 112. ThePVDF material forming each piezoelectric sensor 112 may be adhered tothe outer surface of a steel strap that extends around and clamps ontothe outer surface of the pipe 112. The piezoelectric sensing element istypically conformal to allow complete or nearly complete circumferentialmeasurement of induced strain. The sensors can be formed from PVDFfilms, co-polymer films, or flexible PZT sensors, similar to thatdescribed in “Piezo Film Sensors technical Manual” provided byMeasurement Specialties, Inc. of Fairfield, N.J., which is incorporatedherein by reference. The advantages of this technique includenon-intrusive flow rate measurements, low cost, a measurement techniquerequires no excitation source (i.e. ambient flow noise is used as asource), flexible piezoelectric sensors can be mounted in a variety ofconfigurations to enhance signal detection schemes (these configurationsinclude a) co-located sensors, b) segmented sensors with opposingpolarity configurations, c) wide sensors to enhance acoustic signaldetection and minimize vortical noise detection, d) tailored sensorgeometries to minimize sensitivity to pipe modes, e) differencing ofsensors to eliminate acoustic noise from vortical signals) and highertemperatures (140 C) (co-polymers).

It should be appreciated that the present invention can be embodied inthe form of computer-implemented processes and apparatuses forpracticing those processes. The present invention can also be embodiedin the form of computer program code containing instructions embodied intangible media, such as floppy diskettes, CD-ROMs, hard drives, or anyother computer-readable storage medium, wherein, when the computerprogram code is loaded into and executed by a computer, the computerbecomes an apparatus for practicing the invention. The present inventioncan also be embodied in the form of computer program code, for example,whether stored in a storage medium, loaded into and/or executed by acomputer, or transmitted over some transmission medium, such as overelectrical wiring or cabling, through fiber optics, or viaelectromagnetic radiation, wherein, when the computer program code isloaded into and executed by a computer, the computer becomes anapparatus for practicing the invention. When implemented on ageneral-purpose microprocessor, the computer program code segmentsconfigure the microprocessor to create specific logic circuits.

It should be further appreciated that any of the features,characteristics, alternatives or modifications described regarding aparticular embodiment herein may also be applied, used, or incorporatedwith any other embodiment described herein. In addition, it iscontemplated that, while the embodiments described herein are useful forhomogeneous flows, the embodiments described herein can also be used fordispersive flows having dispersive properties (e.g., stratified flow).Although the invention has been described and illustrated with respectto exemplary embodiments thereof, the foregoing and various otheradditions and omissions may be made therein and thereto withoutdeparting from the spirit and scope of the present invention.

1. An apparatus for determining at least one characteristic of a fluidflowing within a pipe, the apparatus comprising: at least one sensingdevice, wherein said at least one sensing device includes a first sensorsegment having a first segment polarity and being associated with afirst outer portion of the pipe and a second sensor segment having asecond segment polarity and being associated with a second outer portionof the pipe, wherein said first sensor segment and said second sensorsegment generate sensor data responsive to the fluid flowing within thepipe; and a processing device communicated with said at least onesensing device, wherein said processing device receives said sensor dataand processes said sensor data to determine the at least onecharacteristic of the fluid.
 2. The apparatus of claim 1, wherein saidfirst outer portion of the pipe is disposed oppositely said second outerportion of the pipe and wherein said first segment polarity is oppositesaid second segment polarity.
 3. The apparatus of claim 1, wherein saidat least one sensing device further includes a third sensor segmenthaving a third segment polarity and being associated with a third outerportion of the pipe and a fourth sensor segment having a fourth segmentpolarity and being associated with a fourth outer portion of the pipe.4. The apparatus of claim 3, wherein said first outer portion of thepipe is disposed oppositely said third outer portion of the pipe andwherein said second outer portion of the pipe is disposed oppositelysaid fourth outer portion of the pipe.
 5. The apparatus of claim 4,wherein said first segment polarity is equal to said third segmentpolarity and wherein said second segment polarity is equal to saidfourth segment polarity.
 6. The apparatus of claim 3, wherein said firstsensor segment is connected with said third sensor segment via saidsecond sensor segment in a series fashion and wherein said fourth sensorsegment is connected with said second sensor segment via said thirdsensor segment is a series fashion.
 7. The apparatus of claim 1, whereinsaid at least one sensing device includes a plurality of sensor segmentseach of which include a sensor segment length, wherein when said atleast one sensing device is configured to filter out acoustic signals,temperature signals and common mode signals, said sensor segment lengthis sized such that the relationship between said acoustic signals, saidtemperature signals and said common mode signals is given by∫₀^(2π)ɛ(θ)𝕕θ = 0, wherein ε(θ) is equal to the signal power.
 8. Theapparatus of claim 1, wherein said at least one sensing device includesa plurality of sensor segments each of which include a sensor segmentlength, wherein when said at least one sensing device is configured tofilter out bending mode signals, said sensor segment length is sizedsuch that the bending mode signals are given by∫_(π + 0)^(θ + π)ɛ(θ)𝕕θ = ∫_(θ + π)^(θ + 2π)ɛ(θ)𝕕θ, wherein ε(θ) isequal to the signal power.
 9. The apparatus of claim 1, wherein the atleast one characteristic is at least one of the velocity and thevolumetric flow rate of the fluid.
 10. The apparatus of claim 1, whereinsaid at least one sensing device includes a plurality of sensing devicesaxially associated with the pipe to form a sensor array.
 11. A methodfor determining at least one characteristic of a fluid flowing within apipe, the method comprising: receiving sensor data from at least onesensing device, wherein said at least one sensing device includes afirst sensor segment and a second sensor segment disposed in the sameaxial plane, said first sensor segment being associated with a firstouter portion of the pipe and a second sensor segment associated with asecond outer portion of the pipe; and processing said sensor data togenerate the at least one characteristic of the fluid flowing within thepipe.
 12. The method of claim 11, wherein said at least one sensingdevice includes a plurality of sensor segments configured to beassociated with an outer portion of the pipe in the same axial plane.13. The method of claim 11, further comprising a third sensor segmentand a fourth sensor segment disposed in said same axial plane as saidfirst sensor segment and said second sensor segment, wherein said thirdsensor segment is connected to said first sensor segment via said secondsensor segment in a series fashion and wherein said fourth sensorsegment is connected to said second sensor segment via said third sensorsegment in a series fashion.
 14. The method of claim 13, wherein saidfirst sensor segment and said third sensor segment are of a firstsegment polarity and said second sensor segment and said fourth sensorsegment are of a second segment polarity, said first polarity beingopposite to said second polarity.
 15. The method of claim 11, whereinsaid first sensor segment includes a first segment polarity and whereinsaid second sensor segment includes a second segment polarity, saidfirst segment polarity being opposite to said second segment polarity.16. The method of claim 11, wherein said at least one sensing deviceincludes a plurality of sensor segments each of which include a sensorsegment length, wherein when said at least one sensing device isconfigured to filter out acoustic signals, temperature signals andcommon mode signals, the relationship between said acoustic signals,said sensor segment length is sized such that said temperature signalsand said common mode signals is given by ∫₀^(2π)ɛ(θ)𝕕θ = 0, wherein ε(θ)is equal to the signal power.
 17. The method of claim 11, wherein saidat least one sensing device includes a plurality of sensor segments eachof which include a sensor segment length, wherein when said at least onesensing device is configured to filter out bending mode signals, saidsensor segment length is sized such that the bending mode signals aregiven by ∫_(π + 0)^(θ + π)ɛ(θ)𝕕θ = ∫_(θ + π)^(θ + 2π)ɛ(θ)𝕕θ, whereinε(θ) is equal to the signal power.
 18. The method of claim 11, whereinsaid processing includes processing said sensor data to determine atleast one of the velocity and the volumetric flow rate of the fluid. 19.The method of claim 11, wherein said at least one sensing deviceincludes a plurality of sensing devices axially associated with the pipeto form a sensor array.
 20. A sensing device for determining at leastone characteristic of a fluid flowing within a pipe, the sensing devicecomprising: a first sensor segment, and a second sensor segment, whereinsaid first sensor segment and said sensor second segment are associatedwith the pipe to measure unsteady pressure associated with the fluidflow and configured to filter out at least one of acoustic mode signalsand bending mode signals.
 21. The sensing device of claim 20, whereinsaid first sensor segment includes at least one of a first sensorsegment area and a first sensor segment length and wherein said secondsensor segment includes at least one of a second sensor segment area anda second sensor segment length, wherein at least one of said firstsensor segment area is equal to said second sensor segment area and saidfirst sensor segment length is equal to said second sensor segmentlength.
 22. The sensing device of claim 20, wherein said first sensorsegment includes a first sensor segment polarity and said second sensorsegment includes a second sensor segment polarity, said first sensorportion polarity being opposite said second sensor portion polarity. 23.The sensing device of claim 20, wherein said first sensor segment andsaid second sensor segment are configured to satisfy at least one of afirst equation and a second equation, wherein said first equationdescribes the relationship between acoustic signals, temperature signalsand common mode signals as being given by ∫₀^(2π)ɛ(θ)𝕕θ = 0, and whereinsaid second equation describes the bending mode signals as being givenby ∫_(π + 0)^(θ + π)ɛ(θ)𝕕θ = ∫_(θ + π)^(θ + 2π)ɛ(θ)𝕕θ, wherein ε(θ) isequal to the signal power.